Voting by the United Kingdom’s Conservative Party members for their leadership position and the prime minister’s post has been delayed after an intelligence agency warned that cyber hackers could change ballots, The Telegraph reported on Tuesday.

The United Kingdom’s Government Communications Headquarters gave the warning.

The Conservative Party members were informed about the delay in voting on Tuesday night. However, no reason was given for the security concerns.

“Your ballot is now on the way – but it will arrive with you a little later than we originally said,” read a part of the message to party members, according to The Telegraph. “Please do not worry. This is because we have taken some time to add some additional security to our ballot process, which has delayed us slightly.”

The ballots were earlier due to be issued from Monday. Now with the delay in voting, members have been told to inform the party in case their ballots do not arrive even by August 11.

An unidentified spokesperson for the National Cyber Security Centre, which is part of the Government Communications Headquarters, confirmed the delay in the vote to Reuters.

“Defending UK democratic and electoral processes is a priority for the NCSC and we work closely with all Parliamentary political parties, local authorities and MPs to provide cyber security guidance and support,” the spokesperson said. “As you would expect from the UK’s national cyber security authority we provided advice to the Conservative Party on security considerations for online leadership voting.”

The vote became necessary after Boris Johnson announced his resignation as prime minister on July 7.

On June 6, a no-confidence motion was introduced against Johnson after 54 Conservative Party MPs demanded that he resign. They denounced the parties organised by Johnson and his staff members during lockdowns imposed to contain the spread of coronavirus. The controversy has been famously described as the partygate scandal.

Former British Finance Minister Rishi Sunak and Foreign Secretary Liz Truss are contesting the election to become the Conservative Party’s next leader and the country’s prime minister.

In the fifth round of voting held in mid-July, Sunak, the former chancellor of the exchequer, got 137 votes while Truss got the support of 113 MPs.

According to opinion polls among party members, however, Truss is in the lead, Reuters reported.

The winner will be announced on September 5.